1. Field of the Invention
The invention relates generally to safety razor shaving systems that include razor blade assemblies for mounting on handles via pivotal connections. More particularly, the invention relates to a safety razor which features a pivot point that shifts from a center point pivot (e.g., at the center blade of a triple blade razor, substantially on the shave plane), to a guard-bar pivot, substantially on the shave plane, as shaving forces increase to help prevent nicks and cuts, and provide a smooth shave.
2. Brief Description of the Prior Art
Safety razors are well known that employ blade units with a plurality of blades defining sharpened edges arranged to pass in succession over a skin surface being shaved.
The invention is applicable to safety razors having blade units in the form of cartridges detachably mounted on a handle for replacement when the blade edges have become dulled; and to disposable safety razors having blade unit cartridges, which are permanently attached to a razor handle.
The aforementioned blade unit cartridges (whether permanently affixed to a handle or in the form of a replaceable cartridge), generally comprise a rectangular molded plastic frame with guard and cap surfaces on the lengthwise extending frame parts. Within the opening of the frame the blades are arranged in tandem with their cutting edges parallel to each other and directed towards the guard surface.
It is well known that the so-called shaving geometry of a blade unit is important in determining the shaving performance of the unit. The shaving geometry defines the position and orientation of the blades in relation to other skin contacting parts, in particular the guard and cap of the blade unit.
Well known razor blade assemblies employ spring biased cam followers on razor handles to interact with cam surfaces on the bottoms of razor blade assemblies so as to bias the assemblies to neutral positions relative to the handles.
During shaving, the cartridge assemblies can pivot forward or rearward from the neutral position relative to the handle, and the blade package can thereby follow the contours of the skin surface during shaving.
Examples of commercially available safety razors that include the aforementioned pivoting feature include the Schick Xtreame III (TM) triple blade convenience razor; the Gillette Sensor Excel (TM) safety razor and Gillette's Mach III (TM) safety razor.
The blade cartridges for both the Schick Xtreame III razor and the Gillette Sensor Excel safety razor, pivot about a center point pivot; and the cartridges may pivot in each direction from a neutral position.
A center pivot balances forces to allow one to shave evenly with all three blades of the aforementioned triple blade razors.
The Gillette Mach III safety razor is an example of a razor that features a guard-bar pivot (pivoting takes place on an axis through the guard-bar as opposed to a center point pivot); with the cartridge being capable of pivotal movement in only one direction from its neutral position.
With a guard-bar pivot one obtains a “safer” shave than with a center pivot arrangement since applied loads (e.g., pressing the razor against the skin) are on the guard-bar and not the blades. The guard-bar also facilities stretching of the skin compared with a center pivot system, thereby promoting a safe close shave.
During shaving the blades of a blade unit are subjected to a combination of drag forces and the load forces mentioned hereinbefore. Drag forces are those directed essentially parallel to the shaving plane, and load forces are those forces directed against the blade by the skin in the direction substantially perpendicular to the shaving plane (as hereinbefore indicated happens when the razor is pressed in toward the face).
Generally speaking it is important to locate the pivot point of a razor as close to the shave plane as possible to minimize the over-turning moment due to drag force.
Additionally, by applying the razor against the skin surface under greater load pressure to seek an improved closeness of shave, it is desirable to on one hand utilize all the blades in the razor as uniformly as possible (e.g., to prevent dulling of a particular blade, to achieve the maximum cutting action in a single stroke, etc.); yet achieve and maintain a safe shave so that increasingly applied loads do not cause nicks and cuts. Generally, as the force of shaving (loading) increases, the likelihood of experiencing a nick or a cut increases.
Stated another way, it is desirable to accommodate varying loads by the user during the shaving process, minimize drag, insure a close shave and at the same time assure a safe shave.
Although the prior art systems referred to hereinabove employ pivot mechanisms to achieve maximum shaving performance and safety (with tradeoffs of course depending on the type of pivot system used), the pivot axis in all the known systems remain substantially the same.
This has the effect, for center point pivot systems, of not taking maximum advantage of the skin stretching and protection features of the guard-bar which limit blade exposure and protect against nicks and cuts; while for guard-bar pivot systems, do not taking maximum advantage of the multiple blades available in light loading situations where receiving nicks and cuts are far less likely (the aforementioned “tradeoffs”).
Accordingly, it would be desirable to be able to increase loading on the razor and yet maintain a safe shave in pivoting razor systems by shifting the pivot point from the center to the guard-bar under heavy load.
It would also be desirable to provide a razor, which pivots about the center for an even shave under light loading but pivots about the guard-bar under heavy loading.
It would be desirable to provide a razor, which accommodates varying loads by a user during the shaving process, minimizes drag, insures a close shave and at the same time assures a safe shave.
It would also be desirable to provide a razor which utilizes all the blades in the razor as uniformly as possible to prevent dulling of a particular blade, which achieves the maximum cutting action in a single stroke, etc.; and at the same time achieves and maintains a safe shave so that increasingly applied loads do not cause nicks and cuts.